Before plunging into videoconferencing, a company tested the speed of its internal computer network. The tests were designed to measure how rapidly data moved through the network under a typical load. Eighty files ranging in size from 20 to 100 megabytes (MB) were transmitted over the net-work at various times of day, and the time to send the files (in seconds) recorded. Formulate the SRM with Y given by Transfer Time and X given by File Size.
(a) Plot the residuals versus the x-variable and in time order, as indicated by the column labeled Hours past 8. Does either plot suggest a problem with the SRM?
(b) Compute the Durbin-Watson D statistic. Does it indicate a problem? For a series of this length, any value of D that is more than 12 away from 2 is statistically significant with p-value smaller than 0.01.
(c) Explain or interpret the result of the Durbin-Watson test.